Kinetic Study of PET Recycling into PAT and Ethanediol by Hydrolysis Catalyzed by Protonic Acid H+ and Iron-Fe Catalysts

Abstract

PET - Polyethylene Terephthalate is the main raw material used to manufacture PET - PETE plastic bottles. Since 2015, over 6.9 billion tons of plastic waste have been produced and only round 9% was recycled, 12% was incinerated and 79% accumulated in landfills or in nature. The present study involves recycling PET-based plastic materials into ethanediol and terephthalic acid by hydrolysis using two types of acid catalyst: the protonic H<sup>+</sup> acid sites of citric acid molecules and the Lewis acid sites of Iron-Fe molecules. The set-up used is a reflux system consisting of a 250ml flask placed in the flask heater at a temperature of 144°C, with a straight cooler above it. Monitoring the progress of the reaction consisted in titrating the quantities of recycled PAT-Pure Terephthalic Acid molecules formed and the unsaturation in solution with HF-0.0026N hydrofluoric acid, then deducing the quantities of ethanediol molecules formed. The results recorded with the first experiment using the protonic acid H<sup>+</sup> sites of citric acid molecules as catalyst were quite conclusive; 3.0762E-03 moles of PAT had been regenerated per gram of initial charge per moles of protonic H<sup>+</sup> sites per minute. An optimization test was carried out, enabling us to estimate the quantities of Iron-Fe used in the three other tests with the Lewis Iron-Fe site catalyst, with Iron-Fe weight percentages of 15wt%, 58.42wt% and 92.65wt% respectively. It had been recorded that PET conversion increases slowly but surely with reaction time and that the amount of recycled PAT increases very strongly with the amount of catalyst used. Thus, the molar quantity of PAT regenerated per gram of initial charge per mole of Iron-Fe and per minute for the three quantities of catalyst mentioned above are respectively 1.1580E-04 (15wt%), 1.7809E-04 (58.42wt%) and 9.0591E-03 (92.65wt%), i.e. an increase at both ends of 7.723.06% compared with the 15wt% value. Kinetic study had been carried out on the test with 58.42wt% Iron-Fe catalyst, enabling not only to the determination of various kinetic constants but also the validation of a proposed reaction mechanism.